This new project seeks to extend the work on neuropsychological assessment accomplished in the Program's initial period of funding. Its objective is to extend the current method of quantitative performance evaluation of ADC, focussing on more sensitive measures that might prove valuable in multidisciplinary studies directed at the underlying pathophysiological mechanism of ADC. Starting with a well-standardized procedure, this project will establish the utility of a Continuous Performance Task (CPT), using a reaction time measure of sustained attention to characterize ADC. The utility of CPT as a sensitive, early measure of treatment effects in studies of anti-retroviral therapy and of therapies directed at potential neuropathophysiological mechanisms of ADC will also be studied. As a correlate of the CPT measure, its corresponding event related potential (ERP) will also be studied with respect to ADC. Both the CPT and event related potential measures will be studied during FDG/PET scanning in collaboration with Project 4. The objective of these studies is not to replace the previously established methods of the neuropsychological assessment of ADC, but to develop more sensitive measures of impairment in this syndrome that can play a significant role in studying treatment effects and potential pathophysiological mechanisms. In the context of this Program, these studies will be integrated with the studies of regional cerebral metabolism, quantitative MRI, and EEG power spectra, and will play an important role in correlative studies using surrogate markers of direct and indirect effects of HIV-1 infection of the CNS.